bxcore, loopd, inferproxy: a lock file keeps each to one instance

Co-Authored-By: ornith-1.5-35b-a3b <agent@wntrmute.dev>

crates/loopd/src/main.rs

@@ -8,6 +8,7 @@ use std::process::ExitCode;
 use std::sync::Arc;
 use std::time::Duration;
 
+use bxcore::instance;
 use loopd::broker_port::{BrokerPort, NoBroker, not_configured_line};
 use loopd::channel::{self, Context};
 use loopd::config::Config;
@@ -73,6 +74,18 @@ fn run_serve(path: &Path) -> ExitCode {
         }
     };
 
+    // One loopd per home (M5b spec, section 9a). The lock comes before the socket is touched and
+    // before the self-test, so a second copy neither takes the socket of the one that runs nor
+    // sends its slot a prompt. Held until the process ends.
+    let lock_path = cfg.paths.home.join("run/loopd.lock");
+    let _instance = match instance::lock(&lock_path) {
+        Ok(held) => held,
+        Err(e) => {
+            eprintln!("{}", e.line("loopd", &lock_path));
+            return ExitCode::from(1);
+        }
+    };
+
     let socket = cfg.channel_socket();
     if socket.exists()
         && let Err(e) = std::fs::remove_file(&socket)